Researchers at ETH Zurich have developed ultra-flexible brain probes that can record brain activity over long periods without damaging the surrounding tissue. Published in Nature Communications, the study demonstrates how these innovative electrodes could advance treatments for neurological and psychiatric disorders by offering detailed, long-term monitoring of brain activity.
“Our electrodes are so fine that they can be threaded past the long processes that extend from the nerve cells in the brain,” said Mehmet Fatih Yanik, Professor of Neurotechnology at ETH Zurich, who led the research. “They are only around as thick as the nerve-cell processes themselves.”
The researchers conducted this study to overcome the limitations of existing brain-monitoring technologies. Traditional electrodes, used in devices like neurostimulators or “brain pacemakers,” are often rigid and too wide, posing risks of tissue damage when implanted. These devices are already used to treat conditions such as Parkinson’s disease, but their potential is limited by their inability to provide detailed and safe long-term recordings.
Yanik’s team sought to develop an alternative that could collect high-quality brain signals over extended periods, offering new opportunities for diagnosing and treating neurological conditions. “Our goal was to create electrodes that could record brain activity with great precision, but without causing inflammation or damage, as current technologies often do,” Yanik explained.
To achieve this, the team designed electrodes made from ultra-thin, flexible gold fibers encased in a polymer. The fibers, which are only as thick as the processes of nerve cells themselves, are much smaller than current electrode technologies. This delicate design minimizes the risk of damaging the brain when inserted. To further reduce any potential harm, the researchers developed a method to slowly insert the probes into the brain, allowing the fibers to weave through the tissue gently.
The researchers tested the new probes in rats, inserting bundles of 64 fibers into various brain regions. These fibers were connected to a small recording device mounted on each rat’s head, allowing the animals to move freely while their brain activity was monitored. The electrodes were then able to record signals from the same cells in the rats’ brains for up to 10 months without any noticeable damage to the brain tissue.
One of the most important findings from the study was that these new probes are biocompatible, meaning they do not interfere with normal brain function. In fact, the electrodes were able to record high-quality signals due to their proximity to nerve cells.
Over the 10-month experiment, the probes maintained their performance, providing consistent and detailed recordings from the same brain cells. This longevity is a major improvement over current technologies, which often see a decline in signal quality over time due to tissue damage or immune responses.
The flexibility of the electrodes also allowed the researchers to monitor different regions of the brain simultaneously. This is particularly important for understanding how different brain areas work together. In their experiments, the researchers tracked and analyzed nerve cell activity in several regions of the rats’ brains. They found that nerve cells in different regions were often “co-activated,” meaning they fired together. This large-scale, synchronized activity is believed to be essential for processing complex information and forming memories.
“The technology is of high interest for basic research that investigates these functions and their impairments in neurological and psychiatric disorders,” Yanik said.
Despite the promising results, the study does have limitations. Most notably, the testing has so far been limited to animals, and human trials are still in the planning stages. While the electrodes appear to be safe for long-term use in rats, it remains to be seen how they will perform in humans over extended periods. The long-term effects of the implants will need to be thoroughly evaluated, particularly in terms of whether they can continue to function without causing damage to human brain tissue.
Additionally, while the flexibility of the probes offers many advantages, it also poses challenges. For example, the fibers are so thin that inserting them into deeper brain regions in larger animals or humans may require even more advanced surgical techniques. The team is already working on refining the technology to address these challenges and improve the overall ease of use.
Looking ahead, the researchers are planning to test the electrodes in humans. They have partnered with University College London to use the new probes in epilepsy patients who do not respond to drug treatments. In these cases, neurosurgeons often remove a small section of the brain where seizures originate. The team hopes their probes will help pinpoint the exact location of the problematic brain tissue, improving the precision of these surgeries.
The potential applications of these probes extend beyond epilepsy. The electrodes could also be used to treat psychiatric disorders such as depression, schizophrenia, or obsessive-compulsive disorder. Many of these conditions are associated with abnormal brain activity in specific regions. By detecting these abnormal signals early, it may be possible to correct them using electrical stimulation.
“This could aid the development of more effective therapies for people with neurological and psychiatric disorders,” said Yanik.
The study, “Months-long tracking of neuronal ensembles spanning multiple brain areas with Ultra-Flexible Tentacle Electrodes,” was authored by Tansel Baran Yasar, Peter Gombkoto, Alexei L. Vyssotski, Angeliki D. Vavladeli, Christopher M. Lewis, Bifeng Wu, Linus Meienberg, Valter Lundegardh, Fritjof Helmchen, Wolfger von der Behrens , and Mehmet Fatih Yanik.
